The present invention relates to methods for drilling and treating well bores. More particularly, the present invention relates to methods for drilling well bores penetrating producing zones while controlling formation particulates.
Often, well bores are drilled into weakly consolidated formations wherein the walls of the well bore may be sensitive to degradation by the force of mobile fluids within the formation. Often, such well bores are subjected to some form of sand control operation, such as gravel packing, to reduce the migration of unconsolidated formation particulates. One common gravel packing operation involves placing a gravel pack screen in the well bore and packing the surrounding annulus between the screen and the well bore with particulates, referred to as “gravel,” that have a specific size designed to prevent the passage of formation sand. The gravel pack screen is generally a filter assembly used to, among other things, support and retain the gravel placed during gravel pack operations. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel pack sand used. Similarly, a wide range of sizes of gravel is available to suit the characteristics of the unconsolidated or poorly consolidated particulates in the subterranean formation. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid flow. When installing the gravel pack, the gravel is carried to the formation in the form of a slurry by mixing the gravel with a transport fluid. Gravel packs act to, among other things, stabilize the formation while causing minimal impairment to well productivity. The gravel, among other things, acts to prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen, among other things, acts to prevent the gravel from entering the production tubing. While gravel packs have been successfully used to control the migration of formation sands, their placement tends to reduce the available diameter of a well bore due to the physical size of the screen and the gravel packed therein.
The screen assembly referred to in the gravel packing operation may also be used as an independent sand control means. Some of the early screen technology dictated that the screens had to be small enough to pass through the smallest diameter of the well bore on the way to its desired placement location where the diameter of the well bore may actually be larger. Developments in technology have lead to deformable and expandable screens such that a relatively small size or small diameter screen may be placed in a desired location along the well bore and then expanded to accommodate the actual size of the well bore at the point of placement.
While the sand control methods mentioned above are routinely used in the completion of well bores, particularly those drilled into weakly consolidated formations, they increase the expense of installing a well bore by requiring separate steps to drill the well bore and then to control the formation sands.